Method for data transmission by means of a field bus of an automation device

ABSTRACT

A method for transferring data via a field bus FB of an automation system, to which field bus multiple field devices D 1 , D 2 , D 3 , . . . ,Dn, V 1 , V 2 , V 3 , . . . ,Vn are connected. The field bus FB has multiple data channels, to which the field devices have simultaneous access.

The invention concerns a method for transferring data via a field bus ofan automation system, in accordance with the preamble of claim 1.

In the field of automation technology, field devices are frequently usedwhich register or influence process variables in an automation system.Examples of such field devices are flow meters, temperature meters, andpressure meters. These register the corresponding process variables—e.g.flow rate, temperature, and pressure. Such field devices are alsoreferred to as sensors. Valves are an additional field-device category,and, as actuators, influence the flow rate in a section of pipeline.

Generally, the field devices are connected with a control unit (e.g. aprogrammable logic controller, or PLC for short) via a field bus. Thefield bus is also usually connected with superordinated firm networks,which enable the process flow to be monitored and observed.

Conventional field busses (Profibus®, Foundation Fieldbus®, etc.)operate by time multiplexing, that is, at a given point in time, onlyone bus participant can access the bus, and thus transmit data. This isproblematic in the case of very rapid process flows, in which data fromdifferent sensors must be registered quasi-simultaneously, and theassociated valves must also be actuated simultaneously. Such rapidprocess flows are found, for example, in bottling plants, especially inthe case of round bottling machines. In bottling plants, it is a matterof filling a product into a container in an exactly metered,predetermined amount in a very short time. The filling times for acontainer can lie between 0.1 and 1 second.

In the case of round bottling machines, multiple filling stations arearranged circularly on a carousel, and must be actuated in shortseparations in time.

A further disadvantage in the case of round bottling machines is that anelectrical connection between a locationally fixed mechanism and amechanism on the carousel can only be achieved via slip contacts. Thepower supply of the electrical mechanisms found on the carousel is alsoaccomplished via such slip contacts.

In the case of conventional field bus systems (Profibus® FoundationFieldbus®, etc.), a rapid and secure data transfer using slip contactsduring operation is not possible. For this reason, a field bus is alwaysconfined to the area of the carousel, i.e. the controller which controlsthe filling must also be arranged on the carousel. This means, however,at the same time, that the controller operates completelyself-sufficiently, and cannot be influenced from the outside.

In the case of errors that may occur, for example the overfilling of acontainer always at one filling station, or for adjustment, e.g. adensity correction in the case of Coriolis mass flow meters, thebottling system must be stopped and the appropriate changes to thecontroller or the field devices carried out. The availability of thesystem is thereby diminished, which results in not insignificant costs.

An object of the present invention is to provide a method fortransferring data using a field bus of an automation system, whichmethod does not have the above-mentioned disadvantages, and whichespecially enables a rapid and secure data transfer.

This object is achieved through the method defined in claim 1. Anessential idea of the invention is to make multiple data channelsavailable on the field bus for the field devices, such that multiplefield devices have simultaneous access to the field bus.

Advantageous further developments are given in the dependent claims.Advantageously, the access to the data channels is accomplished by thefrequency-multiplexing method. An example of such afrequency-multiplexing method is the OFDM (Orthogonal Frequency DomainMultiplex) method, which is very robust against disturbances.

Advantageously, field devices are connected together in pairs, with eachpair having its own assigned data channel on the data bus. A permanentcorrelation between sender and receiver is thus provided.

An example of a paired correlation is a flow meter and a valve in abottling system. The connection between a locationally fixed controllerand the moving field devices is accomplished via a slip ring.

The invention will now be described in greater detail on the basis of anexample of an embodiment illustrated in the drawing, the figures ofwhich show as follows:

FIG. 1 a schematic illustration of a round bottling machine;

FIG. 2 a schematic illustration of a filling station of a round bottlingmachine according to FIG. 1;

FIG. 3 communication connection on a round bottling machine according toa first variant of the invention; and

FIG. 4 communication connection on a round bottling machine according toa second variant of the invention.

In FIG. 1, the illustrated bottling system includes a round bottlingmachine with multiple filling stations A1, A2, A3 . . . An, arrangedcircularly on a carousel K. The axis of rotation of carousel K isdenoted by DA. At the axis of rotation DA, a slip ring SR is arranged,from which data lines DL1, . . . ,DLn lead to their associated fillingstations A1, . . . ,An. The slip ring SR is connected via a data line DLwith a modem M, to which a computing unit RE is connected.

Each filling station is identically constructed. FIG. 2 shows, by way ofexample, the station A1, with a flow meter D1, which measures thequantity, or amount, of the product to be filled, measured in terms ofvolume or mass, as the case may be. The fill quantity is controlled viaa valve V1, which is also located in a supply line R1. Product supply tothe filling station A1 is accomplished via the supply line R1. Acontainer B1 (sketched as a bottle) is arranged below the outlet ofsupply line R1.

After the filling, the full container B1 is conveyed away from thefilling station A1, and a new, empty container is conveyed to it. Theresidence time of a container at a filling station can lie in the rangeof 0.1 to 1 second. In the case of large round-bottling-machines, up to10,000 bottles per hour can be filled.

Actuation of valve V1 is accomplished either from a control unit S, orfrom the associated flow meter D1, via the data line DL1. For this, theinformation of the flow meter D1 is evaluated in the control unit S, orin the flow meter D1 itself. Valve V1 is actuated such that the quantityof the filled product exactly equals the desired quantity. Here,especially the amount of after-run of the valve must be taken intoaccount. The control signal for the valve must be produced before theflow meter D1 has measured the desired quantity, since the valve V1 hasa finite reaction time, and thus always has a certain amount ofafter-run.

FIG. 3 illustrates schematically a communication connection for a roundbottling machine. A data bus DB has a pair of lines L1, L2, which areconnected with all of the field devices on the carousel K.Communications and power supply of the field devices are accomplishedvia the pair of lines L1, L2. Line L1 is connected with the modem M andcomputing unit RE via a supply slip ring VSR. In the case of thisvariant as illustrated, the field devices control the filling processwithout an additional control unit S. Appropriate algorithms can beimplemented in the field devices. Through the connection with thecomputing unit RE, the field devices can also be accessed while inoperation, in order to carry out particular adjustments.

A further variant of a communication connection is illustrated in FIG.4. Here, the pair of lines L1, L2 is connected only with the flow metersD, a control unit S, and, via the supply slip ring VSR, with the modem Mand the computing unit RE. The control unit S controls valves V1, . . .,Vn via control lines S1, . . . ,Sn, respectively. Here, the controlunit S is arranged on the carousel K.

The variants of FIGS. 3 and 4 reference the flow meters D with “Dmag++”, which is an abbreviation for the Dosimag electromagnetic flowmeasuring device of the assignee, with the “++” indicating provision forpossible future model numbers. FIGS. 3 and 4 also indicate that eachfield device attached to the bus has an address, “Addr.: 1”, etc.

The method of the invention will now be described in greater detail asfollows.

Because the filling time for each container is relatively short, andeach filling station must exchange data in parallel between its flowmeter, the computing unit RE, and its valve, the field bus has multipledata channels, to which the field devices have simultaneous access.

An opportunity for simultaneous access to a field bus is provided by thefrequency-multiplexing method. A very secure and robust method for datatransfer is the OFDM-method.

In the case of filling systems, it has proven especially favorable wheneach flow meter D and its associated valve V are connected via theirown, one, data channel.

Via the computing unit RE, changes to the settings of the field devicesor the control unit S can be carried out, without interrupting theoperation of the round bottling machine.

The OFDM (Orthogonal Frequency Domain Multiplex)-method forms thephysical layer in the OSI (Open Systems Interconnect) Reference Model.For this, the protocols superimposed on this layer, such as Profibus®,Foundation Fieldbus®, etc., are independent.

The invention thereby distinguishes itself in that multiple fielddevices can communicate simultaneously via one data bus, which, in thecase of time-critical applications, is of great importance. With theOFDM-method, a robust method for data transfer is available, which isalso suitable for data busses that have slip contacts as connectionelements.

Translation of German Words in the Drawings

FIG. 1:

-   Change “DLu” to --DLn--;-   change “Schleifring” to --slip ring--;-   change “(Karussel)” to --(carousel)--;-   change “Drehachse” to --rotation axis--; and-   change “Frequenzmultiplex Modem” to --frequency-multiplexing    modem--.    FIG. 3:-   Change “Vent”, each occurrence, to --Valve--.    FIG. 4:-   Change “Abgriff PLC” to --Logging PLC--; and-   change “Vent”, each occurrence, to --Valve--.

1-7. (canceled)
 8. A method for transferring data via an automationsystem field bus, to which multiple field devices D1, D2, D3, . . . ,Dn,V1, V2, V3, . . . ,Vn are connected, comprising the steps of: providingthe field bus FB with multiple data channels; and providing simultaneousaccess for the field devices D1, D2, D3, . . . ,Dn, V1, V2, V3, . . .,Vn to the multiple data channels.
 9. The method as claimed in claim 8,wherein: said simultaneous access to the data channels is accomplishedby frequency-multiplexing.
 10. The method as claimed in claim 9,wherein: an OFDM-method is used as for frequency-multiplexing.
 11. Themethod as claimed in claim 8, further comprising the step of: connectingthe multiple field devices D1, D2, D3, . . . ,Dn, V1, V2, V3, . . . ,Vnin pairs, each pair having its own assigned data channel.
 12. The methodas claimed in claim 11, wherein: in each case, one field device D1, D2,D3, . . . ,Dn, and one valve V1, V2, V3, . . . ,Vn form a pair.
 13. Themethod as claimed in claim 8, wherein: the automation system is abottling plant.
 14. A field device for process automation technology,comprising in combination: a field bus with multiple data channels towhich the field device has simultaneous access with other like fielddevices.